JP2007147934A - Optical controller and optical control system using same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a reflection type optical controller which is improved in the availability of light rays. <P>SOLUTION: The optical controller 100 has a substrate 300, a first reflective layer 32, an optical modulation film 34 which varies in refractive index with an applied electric field, a transparent electrode 36, and a second reflective layer 102 having such reflection characteristics that a reflection band and a transmission band are abruptly switched at a specified wavelength. A Fabri-Perot resonator comprising the first reflective layer 32, optical modulation film 34, transparent electrode 26, and second reflective layer 102 has its resonance wavelength set almost to the specified wavelength. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a light control device using an electro-optical material whose refractive index changes with application of an electric field, and a light control system using the same.

  In recent years, as a large-capacity recording method, a digital information recording system using the principle of a hologram is known (for example, Patent Document 1).

As a material for the spatial light modulator of the hologram recording apparatus, a material having an electro-optic effect such as lead lanthanum zirconate titanate (hereinafter referred to as PLZT) can be used. PLZT is a transparent ceramic having a composition of (Pb _1-y La _y ) (Zr _1-x Ti _x ) O ₃ . The electro-optic effect is a phenomenon in which when an electric field is applied to a substance, the substance is polarized and the refractive index changes. When the electro-optic effect is used, the phase of light can be switched by turning on and off the applied voltage. Therefore, a light modulation material having an electro-optic effect can be applied to an optical shutter such as a spatial light modulator.

  Conventionally, bulk PLZT has been widely used for such applications as optical shutters (for example, Patent Document 2). However, it is difficult for optical shutters using bulk PLZT to meet demands for miniaturization and integration, as well as reductions in operating voltage and cost. In addition, since the bulk method for producing bulk PLZT includes a step of processing at a high temperature of 1000 ° C. or higher after mixing raw material metal oxides, when applied to an element formation process, selection of materials and element structure Many restrictions will be added.

For this reason, attempts are being made to apply PLZT, which is a thin film formed on a substrate, to a light control element instead of bulk PLZT. Patent Document 3 describes a display device in which a PLZT film is formed on a transparent substrate such as glass and a comb-shaped electrode is provided thereon. This display device has a configuration in which polarizing plates are provided on both surfaces of a display substrate on which a PLZT film is formed. Here, by connecting the electrode terminal portion of each pixel to an external drive circuit, a desired pixel is driven, and a desired display can be performed by transmitted light from a light source provided on one surface side of the display substrate. It can be done.
JP 2002-297008 A JP-A-5-257103 Japanese Patent Laid-Open No. 7-146657

  However, in order to put a light modulation film such as a PLZT film as described above into practical use as an element such as an optical shutter, a drive circuit for controlling on / off of a voltage applied to the light modulation film is used together with the light modulation film. It needs to be built on the substrate. In that case, the configuration described in Patent Document 3 has a problem that the area where the drive circuit is formed cannot be used as a display area, and an effective display area cannot be sufficiently obtained.

  Further, in the transmissive display device as described above, when visible light is used as irradiation light, there is a problem that the drive circuit cannot be formed on a substrate such as silicon that is opaque to visible light. Furthermore, in the display device described in Patent Document 3, since a polarizing plate is used, light loss due to the polarizing plate occurs.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a reflection-type light control device with improved light utilization efficiency and a light control system using the same.

  In order to solve the above problems, a light control device according to an aspect of the present invention includes a substrate, a first reflective layer provided on the substrate, and an electric field provided on the first reflective layer. A light modulation film whose refractive index changes in response, a transparent electrode provided on the light modulation film, and a reflection characteristic which is provided on the transparent electrode and in which a reflection band and a transmission band are sharply switched at a predetermined wavelength. A resonant wavelength of a Fabry-Perot resonator including a first reflective layer, a light modulation film, a transparent electrode, and a second reflective layer, and a predetermined wavelength. Are set to be substantially the same.

  According to this aspect, the Fabry-Perot resonator in which light incident from the outside is multiply reflected between the two reflective layers is configured by sandwiching the light modulation film and the transparent electrode between the first and second reflective layers. By changing the electric field applied to the light modulation film, the refractive index of the light modulation film can be changed, the resonance wavelength of this resonator can be shifted, and the amount of light reflected from the top surface of the light control device Can be controlled. At this time, the reflection characteristic of the second reflective layer is formed so that the reflection band and the transmission band are sharply switched at a predetermined wavelength, and the predetermined wavelength is set to be substantially the same as the resonance wavelength. The change in reflectance when the resonance wavelength is shifted can be increased. As a result, the on / off ratio of the light control device can be improved and the light utilization efficiency can be improved.

となるように設定してもよい。このとき、共振波長と所定の波長とを略同一とすることができる。 And a predetermined wavelength lambda _c, and the refractive index of the light modulating film n _p, the refractive index and n _i of the transparent electrode, and t _i the thickness of the transparent electrodes, the incident angle of the light entering the light control apparatus The light modulation film when θ _i is the incident angle of light incident on the light modulation film from the transparent electrode, θ _p , the phase change amount of the light reflected by the first reflection layer is φ, and m is the order. the film thickness _{t p} is,

You may set so that. At this time, the resonance wavelength and the predetermined wavelength can be made substantially the same.

  The order m may be an integer in the range of 4 ≦ m ≦ 10. The on / off ratio of the light control device increases in proportion to the film thickness of the light modulation film. However, if the thickness of the light modulation film becomes too large, a larger electric field must be applied in order to obtain a sufficient refractive index change. When the film thickness of the light modulation film is set as described above, a high on / off ratio can be realized with a suitable applied voltage, and the light use efficiency can be improved.

  The second reflective layer may have a stacked structure of a plurality of dielectric films having different refractive indexes. By laminating dielectric films having different refractive indexes to form the second reflective layer, the reflectance can be accurately controlled by the number of layers to be laminated and the material of the dielectric film.

  At least one of the plurality of dielectric films may be a silicon oxide film. Further, at least one of the plurality of dielectric films may be a silicon nitride film. In the case of forming as a silicon oxide film or a silicon nitride film, a film forming technique of a normal silicon semiconductor manufacturing process can be applied as it is.

  The number of laminated dielectric films of the second reflective layer may be 19 or more and 23 or less. At this time, a balance between the shift amount of the resonance wavelength and the steepness of the reflectance change can be achieved, a suitably high on / off ratio can be realized, and light utilization efficiency can be improved.

  The light modulation film may be formed of an electro-optic material whose refractive index changes in proportion to the square of the applied electric field. The electro-optic material may be lead zirconate titanate or lead lanthanum zirconate titanate.

  The light control device described above may be formed on a semiconductor substrate. In this case, since the control circuit of the light control device can be integrated and formed on the semiconductor substrate, the light control device and the control circuit can be downsized.

  Another aspect of the present invention is a light control system. The light control system includes the light control device described above, a light emitting unit that emits light to the light control device, and a light receiving unit that receives light emitted from the light control device. According to this aspect, for example, a hologram recording device or a display device can be realized.

  It should be noted that any combination of the above-described constituent elements and a representation of the present invention converted between methods, systems, etc. are also effective as an aspect of the present invention.

  With the light control device according to the present invention, the light use efficiency can be improved.

(First embodiment)
An outline of the light control apparatus according to the first embodiment will be described. This light control device is a light control device in which the reflectance is changed by applying an external voltage. This light control device has a Fabry-Perot resonator structure, and includes a light modulation film whose refractive index changes in response to application of an electric field, and two reflective layers formed so as to sandwich the light modulation film. . When a control signal is given in a state where light is incident on the light control device, the reflectance of the light control device can be changed, and the intensity of the reflected light can be controlled. Since the light reflected by the light control device has an intensity proportional to the reflectance, it can be used for various applications by recording and detecting the reflected light with a recording medium or a light detection element.

  FIG. 1 is a cross-sectional view of a light control apparatus 10 according to the first embodiment. The light control device 10 includes a substrate 30, a first reflective layer 32, a light modulation film 34, a transparent electrode 36, and a second reflective layer 40.

  The light control device 10 according to the first embodiment is formed on the substrate 30. As a material for the substrate 30, glass, silicon, or the like having a flat surface can be suitably used. For example, in the case of the substrate 30 made of a semiconductor substrate such as silicon, a switching element may be provided on the substrate, and the light control device 10 may be formed thereon. In this case, the light control device 10 and its control circuit can be downsized.

  A first reflective layer 32 is formed on the substrate 30. As a material of the first reflective layer 32, for example, a metal material such as Pt can be suitably used. The thickness of the first reflective layer 32 is about 200 nm. In the first embodiment, the first reflective layer 32 is made of Pt, and the first reflective layer 32 also functions as an electrode for applying an electric field to the light modulation film 34 as will be described later. When the first reflective layer 32 is made of Pt, the reflectance of the first reflective layer 32 is about 50% to 80%.

A light modulation film 34 is provided on the upper surface of the first reflective layer 32. As the material of the light modulation film 34, a solid electro-optic material whose refractive index changes according to the applied electric field is selected. As such an electro-optical material, PLZT (lead lanthanum zirconate titanate), PZT (lead zirconate titanate), LiNbO ₃ , GaA-MQW, SBN ((Sr, Ba) Nb ₂ O ₆ ) or the like is used. In particular, PLZT is preferably used.

Thickness _{t p} of the light modulating film 34 is determined according to the incident angle and the wavelength of the incident light, for example, when the incident light was red light near 650 nm, it is desirable to form in the range of 500nm to 1500 nm. As described later, the electric field applied to the light modulating film 34, to be applied in the thickness direction of the film, with a thickness t _p and 1500nm or less, applying an electric field to obtain a sufficient refractive index change Easy to do. Further, by setting the thickness t _p and above 500 nm, it is possible to obtain a sufficient optical film thickness change.

A transparent electrode 36 is provided on the upper surface of the light modulation film 34. The transparent electrode 36 can be formed of, for example, ITO (Indium Tin Oxide), ZnO, IrO ₂ or the like. If the transparent electrode 36 formed of ITO or ZnO, the thickness _{t i} is set to about 100 nm to 150 nm. In the case of forming with IrO ₂ , it is desirable that the film thickness t _i be thinner, for example, about 50 nm. Since the transparent electrode 36 has a trade-off relationship between the resistance value and the transmittance, the film thickness t _i may be determined experimentally.

A second reflective layer 40 is formed on the upper surface of the transparent electrode 36. The second reflective layer 40 is formed of a dielectric multilayer film, and first dielectric films 42 and second dielectric films 44 having different refractive indexes are alternately stacked. In the following, a refractive index n _H of the dielectric film having a larger refractive index, the refractive index of the dielectric film towards refractive index lower expressed as n _L. As a combination of materials of the first dielectric film 42 and the second dielectric film 44, SiO ₂ (n _L = 1.48) and Si ₃ N ₄ (n _H = 2.0) can be used. When the dielectric multilayer film is formed of a silicon oxide film and a silicon nitride film, the manufacturing process and manufacturing apparatus for the silicon semiconductor integrated circuit can be used as they are.

The dielectric multilayer film can be formed by a plasma CVD (Chemical Vapor Deposition) method. The SiO ₂ film can be grown in a TEOS, O ₂ atmosphere at a temperature of 200 ° C., and the Si ₃ N ₄ film can be preferably grown in a SiH ₄ , NH ₃ atmosphere at a temperature of 200 ° C. The dielectric multilayer film may be formed by ion beam sputtering.

  The film thickness d for one layer of each of the first dielectric film 42 and the second dielectric film 44 is expressed as follows, where λ is the wavelength of light incident on the light control device 10 and n is the refractive index of the dielectric film. = Λ / (n × 4).

For example, when red laser light having a wavelength of 650 nm is used for the light control device 10, the film thickness d1 of the first dielectric film 42 is SiO ₂ (n = 1.48) as the material. d1 = 633 / (4 × 1.48) = about 109 nm. The film thickness d2 of the second dielectric film 44 is about d2 = 650 / (4 × 2) = 81 nm when Si ₃ N ₄ (n = 2.0) is used as the material. The thicknesses d1 and d2 of the dielectric films constituting the second reflective layer 40 are not necessarily designed to be strictly λ / (n × 4).

As a material of the dielectric film, TiO ₃ (n = 2.2) may be used instead of the silicon nitride film. In this case, the thickness d2 of the second dielectric film 44 is about d2 = 650 / (4 × 2.2) = 73 nm.

  In FIG. 1, the reflectance R2 of light incident on the second reflective layer 40 from the light modulation film 34 is designed to be equal to the reflectance R1 of light incident on the first reflective layer 32 from the light modulation film 34. Is preferred. The reflectance R1 is determined by the metal material used for the first reflective layer 32. When Pt is selected, the reflectance R1 is 50 to 80% as described above.

Therefore, at this time, the reflectance R2 is designed to be 50 to 80%. Since the second reflective layer 40 is composed of a dielectric multilayer film, the reflectance R2 varies depending on the wavelength of incident light. As described below, the first reflective layer 32 of the light control device 10, the light modulating film 34, the transparent electrode 36 and the second reflecting layer 40 constitutes a Fabry-Perot resonator, having a resonant wavelength lambda _m. In the light control device 10 according to the first embodiment, at least in the resonant wavelength lambda _m near wavelength bands, to form a second reflective layer 40 such that the reflectance R2 is substantially constant. For example, the reflectivity R1 of the first reflection layer 32 is 80%, when the resonance wavelength lambda _m is 650nm, in the range of about 600 to 700 nm, the reflectivity of the second reflective layer 40 R2 is 80% It is preferable to set as follows.

  The reflectance R2 of the second reflective layer 40 can be adjusted by the material and thickness of the first dielectric film 42 and the second dielectric film 44. In the first embodiment, as shown in FIG. 1, the second reflective layer 40 is formed by alternately laminating three first dielectric films 42 and two second dielectric films 44, respectively. In the second reflective layer 40, the order of stacking the first dielectric film 42 and the second dielectric film 44 may be reversed. In order to finely adjust the reflectance R2, a third dielectric film may be further laminated.

  In the first embodiment, the transparent electrode 36 and the first reflective layer 32 form an electrode pair. The potential of the first reflective layer 32 is fixed to the ground potential, and the potential of the transparent electrode 36 is controlled by the control unit 12.

  The control unit 12 has a function of generating and outputting a control voltage Vcnt that modulates and emits light incident on the light control device 10. The control unit 12 may be built in the substrate 30. The control voltage Vcnt is a signal that takes a binary value of a high level VH or a low level VL. The high level VH is a potential of about 15 to 20 V, and the low level VL is equal to the ground potential.

The operation of the light control apparatus 10 configured as described above will be described. The light control device 10 has a structure in which the light modulation film 34 and the transparent electrode 36 are sandwiched between the first reflection layer 32 and the second reflection layer 40, and constitutes a so-called Fabry-Perot type resonator. The light control device 10, which is a Fabry-Perot resonator, has a reflection characteristic that the reflectance R changes depending on the wavelength of incident light. The reflectance R of the light control device 10 is defined as R = Iout / Iin, where Iin is the intensity of incident light and Iout is the intensity of reflected light. And a wavelength at which the reflectance of the light control device 10 R is the smallest with the resonant wavelength, expressed in lambda _m.

FIG. 2 is a diagram for explaining the resonance wavelength λ _m of the light control apparatus 10. In the figure, the same components as those in FIG. 1 are denoted by the same reference numerals. As shown in FIG. 2, consider a case where incident light 130 enters from above the light control device 10. Here, attention is focused on the reflected light 132 reflected on the boundary surface between the transparent electrode 36 and the second reflective layer 40 and the reflected light 134 reflected on the boundary surface between the first reflective layer 32 and the light modulation film 34.

（１）式において、ｎ_ｉは透明電極３６の屈折率、ｔ_ｉは透明電極３６の膜厚、θ_ｉは光制御装置１０に入射した光の入射角、ｎ_ｐは光変調膜３４の屈折率、ｔ_ｐは光変調膜３４の膜厚、θ_ｐは透明電極３６から光変調膜３４に入射した光の入射角、λは空気中での光の波長、φは第１反射層３２で光が反射するときの位相変化量である。共振波長λ_ｍは、反射光１３２、反射光１３４が弱め合うときなので、次に示す（２）式を満たす必要がある。

（２）式において、ｍは次数であり、正の整数である。（２）式をλ_ｍについて変形すると、（３）式のようになり、共振波長λ_ｍを表すことができる。

The phase difference δ between the reflected light 132 and the reflected light 134 is expressed as in equation (1).

(1) In the equation, the refractive index of _{n i} is the transparent electrode 36, _{t i} is the thickness of the transparent electrode 36, theta _i is the angle of incidence of light incident on the light control device 10, _{n p} is the refractive of the light modulating film 34 rate, film thickness of t _p is the light modulating film 34, the incident angle of theta _p light incident from the transparent electrode 36 to the light modulating film 34, lambda is the wavelength of light in air, phi in the first reflective layer 32 This is the amount of phase change when light is reflected. Since the resonance wavelength λ _m is when the reflected light 132 and the reflected light 134 are weakened, it is necessary to satisfy the following equation (2).

In the formula (2), m is an order and is a positive integer. When the equation (2) is modified with respect to λ _m , the equation (3) is obtained and the resonance wavelength λ _m can be expressed.

As described above, the refractive index n of the light modulation film 34 depends on the electric field E applied to the light modulation film 34. Now, when the first reflective layer 32 is set to the ground potential and the control voltage Vcnt is applied to the transparent electrode 36 (not shown), an electric field E = Vcnt / t is applied to the light modulation film 34 in the thickness direction. When PLZT is used as the light modulation film 34, the amount of change Δn of the refractive index n of the light modulation film 34 and the applied electric field E are
Δn = 1/2 × (n) ³ × R × E ² (4)
The relationship holds. As can be seen from the equation (4), the refractive index of the light modulation film 34 changes in proportion to the square of the applied electric field. Here, R is an electro-optic constant (Kerr constant).

FIG. 3 is a diagram showing the relationship between the wavelength λ of light incident on the light control device 10 and the reflectance R. (I) shown in FIG. 3 is a light control device when the control voltage Vcnt is at a low level VL, that is, when the potential of the transparent electrode 36 and the first reflective layer 32 is the same and no electric field is applied to the light modulation film 34. 10 shows the reflection characteristics. At this time, the resonance wavelength of the light control device 10 is λ _m 1. Changing the control voltage Vcnt to the high level VH, an electric field is applied to E on the light modulating film 34, from (4), the refractive index of the light modulating film 34 changes from _{n p} a _{n p} + [Delta] n. If the refractive index n _p of the light modulating film 34 changes, the equation (3), also changes the resonance wavelength lambda _m, resonant wavelength shifts from lambda _{m 1} to lambda _{m 2.} λ _m 2 is larger than λ _m 1. The reflection characteristic at this time is shown by (II) in FIG.

When the wavelength λ of light incident on the light control device 10 is set to be equal to the resonance wavelength λ _m 1 when the control voltage Vcnt is at the low level VL, the control voltage Vcnt is changed from the low level VL to a certain high level VH. changing the resonance wavelength lambda _m is by shifting from lambda _m 1 to lambda _m 2, the reflectance R of the light control device 10 is changed from _{R m} 1 to _{R m} 2.

  Here, when the electric field E is not applied to the light modulation film 34, the off state and the reflectance of the light control device 10 are Roff, and when the electric field E is applied, the on state and the reflectance of the light control device 10 are Ron. Ron / Roff is defined as the on / off ratio. When the intensity Iin of the incident light is constant, the intensity Iout of the reflected light is proportional to the reflectance R. Therefore, a larger on / off ratio means that the intensity Iout of the reflected light can be accurately controlled, and the light utilization efficiency is high.

Reflectance R of the light control device 10 at the resonant wavelength lambda _m is lower closer the reflectance R2 at the reflectance R1 and the second reflective layer 40 in the first reflective layer 32. Therefore, as described above, the number and material of the dielectric multilayer films of the second reflective layer 40 are adjusted, and the reflectance R1 in the first reflective layer 32 and the reflectance R2 in the second reflective layer 40 are designed to be equal. By doing so, the reflectance R in the off state can be set low and the on / off ratio can be made high.

  As described above, in the light control device 10 according to the first embodiment, the optical switching element that changes the reflectance by changing the electric field applied to the light modulation film 34 and controls the intensity of the reflected light Iout. Can be realized.

  Since the light control device 10 according to the first embodiment has a reflective configuration, it is not necessary to transmit the incident light Iin through the substrate 30. As a result, the light use efficiency can be improved as compared with the conventional transmission type light control device. Further, the light control device 10 has an advantage that the light utilization efficiency is high without requiring a deflecting plate or an analyzer because the intensity Iout of the reflected light is changed by controlling the reflectance R.

(Second Embodiment)
FIG. 4 is a cross-sectional view of the light control apparatus 100 according to the second embodiment. As shown in FIG. 4, the light control apparatus 100 according to the second embodiment includes a substrate 30, a first reflective layer 32, a light modulation film 34, a transparent electrode 36, a second reflective layer 102, Is provided. Note that the same or corresponding components as those in the first embodiment are denoted by the same reference numerals, and redundant description is omitted as appropriate.

In the light control device 100 according to the second embodiment, the configuration of the second reflective layer 102 formed on the transparent electrode 36 is different from the second reflective layer 40 of the light control device 10 according to the first embodiment. Different. In the light control apparatus 10 according to the first embodiment, as described above, the second reflection layer 40 has the second reflectance layer so that the reflectance of the second reflection layer 40 is substantially constant in the wavelength band around the resonance wavelength λ _m of the light control apparatus 10. A reflective layer 40 was formed.

In the light control apparatus 100 according to the second embodiment, the second reflective layer 102 is formed so as to have reflection characteristics in which the reflection band and the transmission band are sharply switched at a predetermined wavelength. Those having such reflection characteristics that the reflection band and the transmission band are sharply switched at a predetermined wavelength are called edge filters. FIG. 5 is a diagram showing the reflection characteristics of the second reflective layer 102. In FIG. 5, λ ₀ is the center wavelength of the edge filter. As shown in FIG. 5, the reflection characteristic of the second reflective layer 102, a transmission band is switched to steep the reflection band at the wavelength lambda _c. The wavelength lambda _c is a wavelength at which the reflectance R is 50%, referred to as cut-off wavelength. In the light control device 100, the resonance wavelength λ _m of the Fabry-Perot resonator including the first reflection layer 32, the light modulation film 34, the transparent electrode 36, and the second reflection layer 102, and the cut and the off wavelength lambda _c is set to be substantially the same. The fact that the resonance wavelength λ _m and the cutoff wavelength λ _c are substantially the same means that the difference between them is within 20 nm.

Returning to FIG. 4, the configuration of the second reflective layer 102 will be described. As shown in FIG. 4, the second reflective layer 102 has a structure in which two dielectric films having different refractive indexes are laminated. From the transparent electrode 36 side, the lower dielectric film 48, the first dielectric film 42, Second dielectric film 44, first dielectric film 42,... (Repeated stacking of first dielectric film 42 and second dielectric film 44), first dielectric film 42, second dielectric The body film 44, the first dielectric film 42, and the top dielectric film 46 are laminated in this order. The upper dielectric film 46, the lower dielectric film 48, and the second dielectric film 44 are made of the same material, and a material having a higher refractive index than that of the first dielectric film 42 is used. As a material for the upper dielectric film 46, the lower dielectric film 48, and the second dielectric film 44, Si ₃ N ₄ (n _H = 2.0) can be used. Further, as the material of the first dielectric film 42, SiO ₂ (n _L = 1.48) can be used.

The film thickness d1 of the first dielectric film 42 and the film thickness d2 of the second dielectric film 44 are formed to be 1 / (4 × n) times the center wavelength λ ₀ of the edge filter shown in FIG. The That is, the film thickness d1 of the second dielectric film 44 is d2 = λ ₀ / (n _H ) so that the film thickness d1 of the first dielectric film 42 is d1 = λ ₀ / (n _L × 4). X4).

Thickness d4 of thickness d3 and lower dielectric layer 48 of the upper dielectric layer 46 is formed to be 1 / (8 × n) times the central wavelength lambda _0. That is, the film thickness d3 of the lower dielectric film 48 is d4 = λ ₀ / (n _H × 8) so that the film thickness d3 of the upper dielectric film 46 is d3 = λ ₀ / (n _H × 8). ).

The change in the reflection band and the transmission band at the cutoff wavelength λ _c becomes steeper as the number of dielectric films stacked in the second reflection layer 102 increases. However, if the number of stacked layers increases, ripples may occur in the vicinity of the cutoff wavelength. Therefore, the thickness of each dielectric film may be finely adjusted to reduce the ripples.

ここで、（５）式におけるｍは次数であり、正の整数であるから、共振波長λ_ｍとカットオフ波長λ_ｃが略同一になるような光変調膜３４の膜厚ｔは、次数ｍによって定まる離散的な値となる。例えば、光変調膜３４の屈折率ｎ_ｐ＝２．３、レーザ光の入射角θ_ｉ＝０°、カットオフ波長λ_ｃ＝６５０ｎｍであるとする。このとき、カットオフ波長λ_ｃと共振波長λ_ｍとが略同一となるためには、光変調膜３４の膜厚ｔ_ｐを、１４１ｎｍ（ｍ＝１）、２８３ｎｍ（ｍ＝２）、４２３ｎｍ（ｍ＝３）・・・と設定する必要がある。なお、上記の計算例においては、第１反射層３２での位相変化量φ＝１．０とし、ｔ_ｉ＝５５ｎｍとしている。 As described above, the second embodiment includes the cutoff wavelength λ _c of the second reflective layer 102, the first reflective layer 32, the light modulation film 34, the transparent electrode 36, and the second reflective layer 102. The resonance wavelength λ _m of the Fabry-Perot resonator is set to be substantially the same. The resonance wavelength λ _m is determined by the above-described equation (3). In the equation (3), when the resonance wavelength λ _m is the cutoff wavelength λ _c and the equation is modified, it can be expressed as the following equation (5).

Here, m in the formula (5) is a degree and is a positive integer, and therefore the film thickness t of the light modulation film 34 such that the resonance wavelength λ _m and the cutoff wavelength λ _c are substantially the same is the order m. It becomes a discrete value determined by. For example, it is assumed that the refractive index n _p of the light modulation film 34 is 2.3, the incident angle θ _i of the laser light is 0 °, and the cutoff wavelength λ _c is 650 nm. At this time, in order to cut-off wavelength lambda _c and the resonance wavelength lambda _m is substantially equal to the thickness _{t p} of the light modulating film 34, 141nm (m = 1) , 283nm (m = 2), 423nm ( It is necessary to set m = 3). In the above calculation example, the phase change amount φ in the first reflective layer 32 is set to 1.0 and t _i is set to 55 nm.

FIG. 6 is a diagram illustrating the reflection characteristics of the light control apparatus 100 according to the second embodiment. In FIG. 6, in addition to the reflection characteristic 110 of the light control apparatus 100 according to the second embodiment, a reflection characteristic 112 of the light control apparatus 10 according to the first embodiment is also shown for comparison. . The reflection characteristics 110 in FIG. 6 are obtained when the film thickness t _p of the light modulation film 34 is 283 nm (m = 2), the incident angle θ _i of the laser light is 0 °, and the number of stacked second reflection layers 102 is 21. Is the reflection characteristic. On the other hand, the reflection characteristic 112 of the light control device 10 according to the first embodiment shown for comparison is as follows: the film thickness t _p = 283 nm of the light modulation film 34, the incident angle θ _i = 0 ° of the laser light, and the second This is a reflection characteristic when the number of layers of the reflective layer 40 is seven.

As shown in FIG. 6, the reflection characteristic 110, as compared with the reflective properties 112, it can be seen that steeply reflectance R is changed at the short wavelength side of the resonance wavelength lambda _m. Also in the light control apparatus 100 according to the second embodiment, the resonance wavelength λ _m is shifted by applying an electric field to the light modulation film 34 as in the light control apparatus 10 according to the first embodiment. Can do. In this case, the resonance wavelength lambda _m is from shifts in the direction in which the resonance wavelength increases as described with reference to FIG. 3, the reflectivity change in the short wavelength side steep second embodiment than the resonance wavelength lambda _m the form The light control apparatus 100 according to the above has a higher reflectance Ron when in the on state than the light control apparatus 10 according to the first embodiment. That is, the light control apparatus 100 according to the second embodiment has an on / off ratio that is higher than that of the light control apparatus 10 according to the first embodiment, and light utilization efficiency is improved.

Figure 7 is a diagram showing a relationship between the shift amount Δλ of the resonant wavelength lambda _m the number of laminations of the second reflective layer 102. The vertical axis in FIG. 7 represents the shift amount Δλ of the resonance wavelength λ _m when the light control device 100 is turned on, and the horizontal axis represents the number of stacked second reflective layers 102. The film thickness t _p of the light modulation film 34 is set to 283 nm, and the incident angle θ _i of the laser beam is set to 0 °. As shown in FIG. 7, in accordance with the number of stacked second reflective layer 102 is increased, there is a tendency to shift Δλ of the resonant wavelength lambda _m is reduced. When the shift amount of the resonance wavelength lambda _m is reduced, the reflectance Ron decreases when the on-state, on-off ratio decreases. However, if too small number of laminations of the second reflective layer 102, this time because the steepness of the change in reflectance at the short wavelength side of the resonance wavelength lambda _m is lost, also on-off ratio decreases. Thus, the shift amount Δλ of the resonant wavelength lambda _m, since the steepness of the change in reflectance at the short wavelength side of the resonance wavelength lambda _m are in a trade-off relationship, the optimal dielectric film of the second reflective layer 102 The number of stacks may be determined experimentally. According to an experiment by the present inventor, when the number of laminated dielectric films of the second reflective layer 102 is in the range of 19 to 23 layers, the balance between the shift amount Δλ of the resonance wavelength λ _m and the sharpness of the reflectance change. Therefore, a suitably high on / off ratio can be realized.

FIG. 8 is a diagram illustrating the reflection characteristics of the light control device 100 when the thickness of the light modulation film 34 is changed. The cutoff wavelength lambda _c of the second reflective layer 102 and 650 nm, and by changing the thickness _{t p} of the light modulating film 34 so that the resonance wavelength lambda _m is 650 nm. Lamination number of the dielectric film of the second reflective layer 102 was set to 21 layers, the incident angle theta _i of the laser beam is 0 °. In FIG. 8, when the reflection characteristic 114 is the film thickness t _p = 283 nm (m = 2) of the light modulation film 34, the reflection characteristic 116 is t _p = 1415 nm (m = 10), and the reflection characteristic 118 is t _This is the reflection characteristic when _p = 2830 nm (m = 20).

As can be seen from FIG. 8, the change in reflectance on the short wavelength side of the resonance wavelength lambda _m is steeper as the thickness t _p of the light modulating film 34 becomes thicker. Therefore, as the thickness t _p of the light modulating film 34 is thick, the resonance wavelength lambda _m is the reflectance changes when the shift is large, on-off ratio of the light control device 100 will be improved.

FIG. 9 is a diagram illustrating the relationship between the on / off ratio of the light control device 100 and the film thickness of the light modulation film 34. The vertical axis in FIG. 9 represents the on / off ratio of the light control device 100. The horizontal axis represents the thickness t _p of the light modulating film 34 by using an order m. (5) As shown in equation, the thickness t _p of the light modulating film 34 becomes a discrete value determined by the order m, the thickness t _p of the light modulating film 34 in each additional the order m becomes thicker. As shown in FIG. 9, the on-off ratio of the light control device 100, in proportion to the degree m, i.e. it can be seen that increases in proportion to the thickness t _p of the light modulating film 34. However, if the film thickness t _p of the light modulating film 34 is too large, it will have to apply a large electric field in order to obtain a sufficient refractive index change. Therefore, the order m is preferably in the range of about 4 ≦ m ≦ 10. If the thickness t _p of the light modulating film is set as described above, can achieve high with a suitable applied voltage OFF ratio, it is possible to improve the utilization efficiency of light.

  As described above, in the light control device 100 according to the second embodiment, the reflection characteristics of the second reflective layer 102 are formed so that the reflection band and the transmission band are sharply switched at a predetermined wavelength. Is set to be substantially the same as the resonance wavelength, it is possible to increase the change in reflectance when the resonance wavelength is shifted. As a result, the on / off ratio of the light control device 100 is improved, and the light utilization efficiency can be improved.

  FIGS. 10A and 10B are diagrams showing a spatial light control device in which light control devices are arranged in a matrix. FIG. 10A shows a plan view of the spatial light control device 8. The spatial light control device 8 includes a plurality of pixels 20 arranged in a two-dimensional array of 8 rows and 8 columns on a substrate 30. The pixel 20 has a size of about 20 μm × 20 μm.

  FIG. 10B is a cross-sectional view taken along the line A-A ′ of the spatial light control device shown in FIG. One pixel 20 corresponds to the light control device 100 shown in FIG. 4, and components such as the light modulation film 34 are the same as those of the light control device 100. In the spatial light control device 8, as shown in FIG. 10B, the transparent electrode 36 is drawn out via the via and the wiring 38. As the material of the wiring 38, Al or the like is preferably used. A protective film may be further formed on the upper surface of the wiring 38.

  The spatial light control device 8 is supplied with the control voltage Vcnt from the control unit 12 for each pixel 20, and can control the reflectance for each pixel 20.

  Various light modulation systems can be configured using the spatial light control device 8. FIG. 11 is a diagram showing a hologram recording device 70 using the spatial light control device 8. The hologram recording device 70 includes a light emitting unit, a light receiving unit, and a spatial light control device 8. The light emitting unit includes a laser light source 72 and a beam expander 74. The light receiving unit includes a Fourier transform lens 76 and a recording medium 78.

  In the hologram recording device 70, the laser light emitted from the laser light source 72 is split into two lights by a beam splitter (not shown). One of these lights is used as reference light and guided into the recording medium 78. The other light is expanded in beam diameter by the beam expander 74 and irradiated to the spatial light control device 8 as parallel light.

  The light applied to the spatial light control device 8 is reflected from the spatial light control device 8 as signal light having different intensities for each pixel. This signal light passes through the Fourier transform lens 76 and is Fourier transformed and collected in the recording medium 78. In the recording medium 78, the signal light including the hologram pattern and the optical path of the reference light intersect to form an optical interference pattern. The entire optical interference pattern is recorded on the recording medium 78 as a change in refractive index (refractive index grating).

  The present invention has been described based on the embodiments. This embodiment is an exemplification, and it is understood by those skilled in the art that various modifications can be made to the combination of each component and each processing process, and such modifications are also within the scope of the present invention. By the way.

  In the embodiment, the case where the light control device 100 is used as the spatial light control device of the hologram recording device 70 has been described. However, the present invention is not limited to this, and the display device, the optical communication switch, the optical communication modulator, and the optical calculation device are used. , And an encryption circuit.

It is sectional drawing of the light control apparatus which concerns on 1st Embodiment. It is a figure for demonstrating resonance wavelength (lambda) m of a light control apparatus. It is a figure which shows the relationship between wavelength (lambda) and the reflectance R of the light which injects into a light control apparatus. It is sectional drawing of the light control apparatus which concerns on 2nd Embodiment. It is a figure which shows the reflective characteristic of a 2nd reflective layer. It is a figure which shows the reflection characteristic of the light control apparatus which concerns on 2nd Embodiment. It is a figure which shows the relationship between the number of lamination | stacking of a 2nd reflective layer, and shift amount (DELTA) (lambda) of resonance wavelength (lambda) m. It is a figure which shows the reflection characteristic of the light control apparatus at the time of changing the film thickness of a light modulation film. It is a figure which shows the relationship between the on-off ratio of a light control apparatus, and the film thickness of a light modulation film. (A) shows the top view of a spatial light control apparatus. (B) shows the A-A 'line sectional view of the spatial light control device shown in (a). It is a figure which shows the hologram recording apparatus using a spatial light control apparatus.

Explanation of symbols

  8 spatial light control device, 10 light control device, 12 control unit, 20 pixels, 30 substrate, 32 first reflective layer, 34 light modulation film, 36 transparent electrode, 38 wiring, 40 second reflective layer, 42 first dielectric Film, 44 second dielectric film, 46 top dielectric film, 48 bottom dielectric film, 60 control unit, 70 hologram recording device, 72 laser light source, 74 beam expander, 76 Fourier transform lens, 78 recording medium, 100 light Control device, 102 second reflective layer;

Claims (11)

A substrate,
A first reflective layer provided on the substrate;
A light modulation film provided on the first reflective layer, the refractive index of which varies according to the applied electric field;
A transparent electrode provided on the light modulation film;
A second reflection layer provided on the transparent electrode and having a reflection characteristic in which a reflection band and a transmission band are sharply switched at a predetermined wavelength;
With
The resonance wavelength of a Fabry-Perot resonator composed of the first reflective layer, the light modulation film, the transparent electrode, and the second reflective layer is substantially the same as the predetermined wavelength. A light control device characterized by being set to be Wherein the predetermined wavelength lambda _c, the refractive index and n _p of the light modulating film, the refractive index and n _i of the transparent electrode, and a thickness t _i of the transparent electrode, enters to the light control apparatus The incident angle of light is θ _i , the incident angle of light incident on the light modulation film from the transparent electrode is θ _p , the phase change amount of light reflected by the first reflective layer is φ, and m is the order when the thickness t _p of the light modulating film,

The light control device according to claim 1, wherein the light control device is set to be   The light control apparatus according to claim 2, wherein the order m is an integer in a range of 4 ≦ m ≦ 10.   4. The light control device according to claim 1, wherein the second reflective layer has a laminated structure of a plurality of dielectric films having different refractive indexes. 5.   The light control apparatus according to claim 4, wherein at least one of the plurality of dielectric films is a silicon oxide film.   The light control apparatus according to claim 4, wherein at least one of the plurality of dielectric films is a silicon nitride film.   7. The light control device according to claim 4, wherein the number of stacked dielectric films of the second reflective layer is 19 or more and 23 or less. 8.   The light control device according to claim 1, wherein the light modulation film is formed of an electro-optic material whose refractive index changes in proportion to the square of an applied electric field.   9. The light control device according to claim 8, wherein the electro-optic material is lead zirconate titanate or lead lanthanum zirconate titanate.   10. The light control device according to claim 1, wherein the light control device is formed on a semiconductor substrate. The light control device according to any one of claims 1 to 10,
A light emitting unit for irradiating light to the light control device;
A light receiving unit for receiving light emitted from the light control device;
A light control system comprising:

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